This invention relates to photographic objectives and more particularly to objectives of standard or quasi-standard field angle.
Triplet objectives of the Tessar type, though widely having used in photographic devices tend to exhibit large longitudinal deviation from an ideal image field in the sagittal plane. At the same time, their astigmatism is quite large.
Various proposals for improving the aberrations of the Tessar type objectives have been made. One of these proposals, disclosed in U.S. Pat. No. 3,011,401 makes use of an additional lens element of bi-convex form positioned at the rear of the objective. With this Tessar type of objective system it is quite difficult to achieve a good compromise between the requirements of increasing the back focal length and of minimizing the various aberrations. Another proposed system is disclosed in Japanese Patent Application Laid-Open No.Sho 51-143326 where the additional lens element is in the form of a positive meniscus lens.